Semester

Spring

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Amy Weislogel

Committee Member

Shikha Sharma

Committee Member

Jaime Toro

Abstract

In the east-central Allegheny foreland basin, laminated black shales overlying Upper Pennsylvanian Glenshaw Fm. coal seams record paleoenvironmental conditions associated with the termination of peat swamp deposition before, during, and after the Carboniferous Coal Forest Collapse (CCFC), a major paleobotanical evolutionary event during the Late Paleozoic Ice Age (LPIA) that contributed to extinction of lepidodendrons near the Desmoinesian-Missourian boundary (~306 Ma). Previous investigations of the CCFC commonly implicate an episode of aridification during intensification of LPIA glaciation that stressed the lepidodendrons beyond their ecological tipping point; however, the cause of this aridification is unclear. An investigation of Glenshaw Fm. black shale geochemistry aimed to assess whether the termination of peat resulted from marine flooding linked to interglacial sea level rise, or development of anoxic aquatic terrestrial environments linked to some other driver. Sedimentological analysis of 9 roofshales at 6 Glenshaw Formation outcrops in West Virginia combined with geochemical analysis of forty samples indicates changes in clastic input, organic carbon content, salinity, and redox-sensitive elements, which constrain environmental dynamics. Shales above the Harlem coal that formed after the CCFC show indicators of low clastic influx, anoxia, moderate weathering, and marine salinity, consistent with termination of peat due to marine flooding. In contrast, shales associated with coal seams that pre-date the CCFC (Upper Freeport) and post-date the CCFC (Wilgus, Bakerstown) all show higher detrital influx values, hypoxic conditions, more intense weathering and primarily non-marine salinity indicators, which is consistent with predominantly nonmarine black shale deposition. These results suggest peat forming environments were replaced by freshwater aquatic terrestrial environments during and after the CCFC and would be consistent with orbital forcing of intense glacial cycles combined with a shift from ever wet climate to seasonally dry climate that could not sustain peat forests as contributing factors to the CCFC.

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